Glossary

A display that consists of two polarizing transparent panels and a liquid crystal surface sandwiched in between. Voltage is applied to certain areas, causing the crystal to turn dark. A light source behind the panel transmits through transparent crystals and is mostly blocked by dark crystals.

LCD or Liquid Crystal Display is widely used in portable computers, digital watches, and, more recently, in home entertainment products. An LCD display consists of a liquid crystal solution suspended between two glass plates. When an electric current is passed through the liquid crystal solution, it causes the crystals to align in a certain configuration. As a result, light can pass through certain crystals and not through others, thereby producing the projected image.

The Lens Shift feature of a projector allows the optical lens to be physically shifted up and down (Vertical) or left and right (Horizontal). With a projector that has lens shift you can optically correct for keystone distorted images. It is also used to help geometrically align images when stacking projectors.

Format used widely on laser disc and many DVDs to fit wide-aspect-ratio movies (1.85:1 and 2.35:1, for example) into a smaller frame, such as the 1.78:1 area of an anamorphic DVD or the 1.33:1 area of a laser disc or video tape. The image is shrunk to fit the screen, leaving blank space on the top and bottom. This process sacrifices some vertical detail that must be used to record the black bars.

(...Tripler, ...Quadrupler) A set of circuits whose purpose is to paint each scan line on the picture tube twice (three times, four times) and thus fill in the gaps between scan lines. A device (with circuits inside) which converts interlaced video to progressive scan video is also referred to as a line doubler. It too delivers output that has twice as many scan lines per second as its input and it may also use the technique equivalent to painting each scan line twice.

Lines of horizontal resolution are often confused with scan lines. The two are totally different things, be careful when shopping for equipment. Lines of horizontal resolution refers to visually resolvable vertical lines per picture height. In other words, it's measured by counting the number of vertical black and white lines that can be distinguished an area that is as wide as the picture is high. Lines of horizontal resolution applies both to television displays and to signal formats such as that produced by a DVD player. Since DVD has 720 horizontal pixels (on both NTSC and PAL discs), the horizontal resolution can be calculated by dividing 720 by 1.33 (for a 4:3 aspect ratio) to get 540 lines. On a 1.78 (16:9) display, you get 405 lines. In practice, most DVD players provide about 500 lines instead of 540 because of filtering and low-quality digital-to-analog converters. VHS has about 230 (172 widescreen) lines, broadcast TV has about 330 (248 widescreen), and laserdisc has about 425 (318 widescreen). Scan lines, on the other hand, measure resolution along the y axis. DVD produces 480 scan lines of active picture for NTSC and 576 for PAL. The NTSC standard has 525 total scan lines, but only 480 to 483 or so are visible. (The extra lines are black and are encoded with other information). Since all video formats (VHS, LD, broadcast, etc.) have the same number of scan lines, it's the horizontal resolution that makes the big difference in picture quality.

The black and white (Y) portion of a composite, Y/C, or Y/Pb/Pr video signal. The luminance channel carries the detail of a video signal. The color channel is laid on top of the luminance signal when creating a picture. Having a separate luminance channel ensures compatibility with black-and-white televisions.

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